<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Promise 多任务串连</title>
</head>
<body>
    <script>
        let p =new Promise((resolve,reject)=>{
            setTimeout(()=>{
                resolve('ok');
            },1000);
        });

        p.then(value=>{
            console.log(value,'11111');  // ok
            return new Promise((resolve,reject)=>{
                resolve('success');
            })
        }).then(value=>{
            console.log(value,'22222');  //sucess
        }).then(value=>{
            console.log(value,'33333');  // undefined  
        })
    </script>
</body>
</html>